1. Field of the Invention
The present invention relates to a rolling mill stand with work rolls which are supported as necessary by back-up rolls or by intermediate and back-up rolls. The work rolls, the intermediate rolls and/or the back-up rolls are axially slidable relative to each other. The bodies of the rolls are provided with alternatingly concavely and convexly shaped contours in such a way that the rolls supplement each other preferably in at least one axial position of the rolls so that preferably no gap exists between the rolls. Corrections of the roll gap profile between a pair of rolls can be carried out by relative axial displacement of the rolls.
2. Description of the Prior Art
A rolled steel strip leaving a cold rolling mill train as a finished product must meet several important requirements. Surface textures should be avoided and the strip should have a constant thickness over its entire length. In addition, in order to avoid unevenness of the strip, it is necessary to roll the strip uniformly over its width, so that internal stresses are avoided which could lead to undesirable undulations in the middle area, the edge area or the quarter area of the strip. The latter can only happen if the roll gap profile under load is correctly adjusted by means of adjusting mechanisms.
It is known, for example, to construct the circumferential surfaces of rolls slightly cambered in order to compensate any roll bending and roll flattening occurring during rolling under the influence of the rolling load. However, such a cambered roll shape is usable only for a given load ratio which is determined by the task to be carried out and the occurring rolling force. When different loads occur, different conditions exist and, thus, an incomplete compensation is carried out. Therefore, in practice, it is necessary to have available rolls of different shapes for different load conditions and to exchange the rolls as required. On the other hand, smaller corrections can be achieved by adjusting the bending of the rolls and possibly by a controlled cooling in certain zones.
German patent 30 38 865 discloses axially slidable rolls of the above-described type which are shaped in such a way that the effect resulting from the contours of two rolls can be determined by the relative axial displacement of the rolls. Thus, as required, practically any parabolic shape can be adjusted for the roll bodies from negative to positive contours of the bodies, so that it is no longer necessary to use different sets of rolls or to exchange the rolls even if the load conditions are substantially changed.
It has been found that the rolls disclosed in German patent 30 38 865, which are bottle-type rolls operating according to the CVC-principle, are capable of compensating parabolic bending over the entire length of the roll bodies, wherein the parabolic bending is determined essentially by quadratic components. However, excessive stretching in the edge area or the quarter area of the strip bridge may lead to undulations in the edge area or the quarter area, can only be reduced by using strong additional bending devices. Usually it is useful to use the bending devices together with cooling in certain zones.
It is therefore, the object of the present invention to provide a rolling mill stand of the above-described type in which it is possible to change roll gaps by merely relatively axially displacing the rolls, so that a steel strip can be obtained which is essentially free of stress and free of undulations.